Two platinum(ii) complexes with a 4-phenyl-4H-1,2,4-triazole derivative as an ancillary ligand for efficient green OLEDs

Abstract

Two new cyclometalated platinum(II) complexes ((TN₃T)Pt(dptp), (4tfmppy)Pt(dptp)) with 2′,6′-bis(trifluoromethyl)-2,3′-bipyridine (TN₃T) and 4-trifluoromethylphenylpyridine (4tfmppy) as the cyclometalated ligands and the nitrogen heterocycle 2-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)phenol (dptp) as the ancillary ligand were developed. Both complexes are green phosphors with high photoluminescence quantum efficiency yields (λ_max = 532 nm, Φ_p = 65% for (TN₃T)Pt(dptp) and λ_max = 502 nm, Φ_p = 71% for (4tfmppy)Pt(dptp)) in CH₂Cl₂ solutions at room temperature, respectively. Organic light-emitting diodes (OLEDs) with single-emitting layer and double-emitting layer structures were fabricated with good performances. Particularly, the double-emitting layer device D2 based on the complex (4tfmppy)Pt(dptp) with 6 wt% doped concentration shows superior performances with a maximum EQE of 26.90% with mild efficiency roll-off. This study demonstrates that the ancillary ligand attached with a 4-phenyl-4H-1,2,4-triazole group could facilitate charge trapping across the bulk of the device for efficient OLEDs.